Technological and environmental problems have persistently arisen as the quest for crude oil and gas becomes more and more acute. Further, it has become necessary to go further offshore in search of adequate production areas. However, the further offshore that one goes, the deeper the water will be.
As a consequence, wellbores are being drilled regularly in greater than one thousand feet of water. While much technology is available regarding the safe and controlled drilling of offshore wells, the problems which arise in conjunction with the deeper waters are becoming increasingly complex.
With the greater depths of water in which it has become necessary to drill, fixed platforms utilized for producing such wells involves enormous costs. It thus reduces to a question of; is the prospective crude oil-containing reservoir beneath the ocean floor sufficiently abundant to warrant the use of expensive deep water drilling and/or producing platforms.
Within the past several years, considerable research and development work has been addressed toward the design and production of usable tension leg platform systems. In the latter type unit, the basic component comprises a floatable vessel which is capable of adjusting its buoyancy at the water's surface.
A plurality of anchors which have previously been positioned at the ocean floor, are connected to the buoyant vessel by a plurality of pull down cables or pipes. It is thus possible, by adjusting the tension on the pull down members, to position the floating vessel above an area in which a well is to be drilled.
The floating vessel will usually be displaced from directly above a drilling site by surface conditions such as wind and waves, as well as by underwater currents. It is nonetheless possible through the use of supported risers or the like to accomplish drilling operations at great water depths through this type of unit.
A problem which is always present when operating in deep offshore waters, is the possibility that the well or wells being drilled can at any time become uncontrolled or blown out and flow without restraint. This situation has occurred in the past and frequently results in loss of equipment due to damage and/or fire. It also results in the loss of the crude product and the gas, both of which flow rapidly to the water's surface.
With the added risk involved in drilling wells in deep waters, it is conceivable that even a minor leak at the ocean floor would permit an uncontrolled and disastrous flow of oil and gas. Such a situation would not only result in the loss of the oil, but could constitute a safety hazard to the immediate environment.
To overcome the above-identified problems and difficulties which are endemic to drilling in deep offshore waters, the present invention is provided. In the latter, a drilling vessel having a floatable hull is positioned at the water's surface upwardly, from a well site. Hold down, variable tension members operably connect to the vessel and extend downwardly to the ocean floor. At the latter the hold down members are connected to a plurality of prepositioned anchors.
A detachably connected ring or collar depends from the vessel's hull and includes means to operably engage the respective hold down members. Thus, in the event that an uncontrollably flowing well is encountered, the submergible ring can be slidably engaged with the hold down means and controllably lowered to the ocean floor. The vessel can then be removed from the area as a safety measure.
The ring includes means to engage the respective anchors, as well as the pull down cables. The ends of the latter are connected to buoys which float at the water's surface to locate the cable ends.
A cap member which defines a substantially fluid tight closure is then drawn by the pull down cables to engage the anchor ring. Uncontrollably escaping effluent can thus be confined, collected, and conducted to the water's surface.
It is therefore an object of the invention to provide an offshore well drilling and/or producing system which is capable of quickly and effectively confining the effluent from an uncontrollably flowing well. A further object is to provide a tension leg platform having means to collect the freely flowing effluent from an uncontrolled well at the ocean floor. A still further object is to provide a tension leg platform system having a detachably held, submergible ring that can be controllably lowered to the ocean floor by way of the platform's hold down means, whereby to receive a closure cap which will confine the well effluent.